1. Field of the Invention
This invention relates to environmental test chamber heating and cooling systems, and more specifically, to an improved system for cooling and heating environmental test chambers using a lower capacity, smaller footprint, refrigeration and heating system in combination with thermal storage.
2. Description of the Related Art
Environmental test chambers subject components within them to a variety of physically challenging test conditions. These test conditions can include acceleration tests, sand or water tests, and temperature tests. The temperature tests can consist of not only extremes of heat and cold, but also tests of large temperature changes in very short periods of time. A typical environmental test chamber system for imposing large temperature changes in very short periods of time may comprise a single or twin section insulated environmental test chamber, and coupled to the environmental test chamber, a large capacity refrigeration system. A large capacity environmental test chamber system is capable of imposing a temperature change from +150xc2x0 C. to xe2x88x9265xc2x0 C. in less than five minutes, and reducing the temperature to xe2x88x9273xc2x0 C. Additionally, slower tests utilizing temperature ramp rates of five, ten, or 20xc2x0 C. per minute, also within this field, still have large system capacity requirements.
A more complete explanation of environmental test methods and standards is detailed in: the Electronics Industries Association""s, (EIA) JEDEC JESD22 group of specifications; Military Specifications Mil-Std 202, Mil-Std 750, Mil-Std 810, and Mil-Std 883; and the IEC pub 68 IEC Standards, all of which are incorporated herein by reference.
The physical plant requirements to produce these temperature changes, whether the very fast temperature ramp rate or the slower ramp rates, are very substantial. A large tonnage refrigeration and/or heating system is required, and the physical size of such a large capacity refrigeration and heating system is correspondingly large. A large tonnage refrigeration and heating system also has substantial energy requirements while it is in operation. An additional problem with conventional environmental test chamber systems is that the temperature transient, from the hot extreme to the cold extreme, for cyclic testing may be very broad i.e. xe2x88x9265xc2x0 C. to +150xc2x0 C. In order to subject the item under test to the desired temperature transition, the item under test in an environmental test chamber system must either: (1) be physically moved from a first pre-heated hot chamber into a second pre-cooled cold chamber, or visa versa, a physical transition that requires two separate and insulated chambers which results in a system with a double size facilities footprint; or (2) for a single chamber environmental test chamber system, the refrigeration and heating system must be larger yet to enable the sudden heat transfer of the item under test""s heat load.
Therefore, a need existed for an improved environmental test chamber refrigeration and heating system that has the requisite temperature transition capabilities utilizing a smaller capacity refrigeration and heating system for single chamber environmental test chambers. Another need existed for an improved environmental test chamber refrigeration and heating system that has the requisite temperature transition capabilities utilizing a smaller capacity refrigeration and heating system for dual chamber environmental test chambers. A further need existed for an improved environmental test chamber refrigeration and heating system having only one insulated environmental chamber thereby eliminating the physical movement of an item under transition temperature testing and also providing a reduced facilities footprint. Yet a further need existed for an improved environmental test chamber refrigeration and heating system having a substantial improvement in energy usage efficiency.
It is an object of the present invention to provide an improved environmental test chamber refrigeration and heating system that has the requisite temperature transition capabilities while utilizing a smaller capacity refrigeration and heating system for single chamber environmental test chambers.
It is another object of the present invention to provide an improved environmental test chamber refrigeration and heating system that has the requisite temperature transition capabilities while utilizing a smaller capacity refrigeration and heating system than would otherwise be required for dual chamber environmental test chambers.
It is a further object of the present invention to provide an improved environmental test chamber refrigeration and heating system having only one insulated environmental chamber thereby eliminating the physical movement of an item under transition temperature testing and also providing a reduced facilities footprint.
It is yet a further object of the invention to provide an improved environmental test chamber refrigeration and heating system having a substantial improvement in energy usage efficiency.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following, more particular, description of the embodiments of the invention, as illustrated in the accompanying drawings.
In the description of the present invention; the following definitions will be used for the respective terms:
Coil
A coil is a heat exchanger that transfers heat; it can be an evaporator, condenser or a reheat heat exchanger depending on the direction of heat flow at the time of use and in the phase change of the refrigerant.
Condenser
In a condenser the refrigerant changes from a vapor to a liquid, lowering it""s heat content in the process.
Evaporator
In an evaporator the refrigerant changes from a liquid to a vapor, raising it""s heat content in the process.
Reheat Heat Exchanger
In a reheat heat exchanger the refrigerant lowers it""s heat content without changing phase. In the use of a reheat heat exchanger herein it is first a condenser then as the chamber warms above the condensing temperature of the refrigerant it can only deliver sensible heat from the refrigerant.
Subcooling
Subcooling means lowering the temperature and thus the heat content of a liquid refrigerant without a change in phase.
According to one aspect of the invention, an environmental test chamber fast cool down and heat up system is disclosed. The environmental test chamber fast cool down and heat up system comprises: an environmental test chamber having a fast cool down evaporator and fast heat up condenser coil, wherein the heat exchanger coil is selectively coupled either to receive a hot refrigerant gas flow or to receive a sub-cooled refrigerant flow; a cascade condenser coupled to the environmental test chamber; a primary stage sub-system coupled to the cascade condenser; a secondary stage sub-system coupled to the cascade condenser; and a thermal storage unit coupled to the primary stage sub-system and to the secondary stage sub-system. Wherein the environmental test chamber has an operational temperature down to about xe2x88x92125xc2x0 F.
According to another aspect of the invention, an environmental test chamber cooling system is disclosed. The environmental test chamber cooling system comprises: an environmental test chamber having a fast cool down evaporator and fast heat up condenser coil, wherein the heat exchanger coil is selectively coupled either to receive a hot refrigerant gas flow or to receive a sub-cooled refrigerant flow; a refrigeration sub-system coupled to the heat exchanger coil; a thermal storage unit coupled to the refrigeration sub-system; wherein the environmental test chamber has an operational temperature down to about xe2x88x92125xc2x0 F.; and wherein the sub-cooled refrigerant flow cools the environmental test chamber down to about xe2x88x92125xc2x0 F.
According to a further aspect of the invention, an environmental test chamber fast cool down and heat up system is disclosed. The environmental test chamber fast cool down and heat up system comprises: an environmental test chamber having a fast cool down evaporator and fast heat up condenser coil, wherein the heat exchanger coil is selectively coupled either to receive a hot refrigerant gas flow or to receive a sub-cooled refrigerant flow; a cascade condenser coupled to the environmental test chamber; a primary stage sub-system coupled to the cascade condenser; a secondary stage sub-system coupled to the cascade condenser; a thermal storage unit coupled to the primary stage sub-system and to the secondary stage sub-system. Wherein the environmental test chamber has an operational temperature down to about xe2x88x92125xc2x0 F.; wherein the primary stage sub-system has up to an enthalpy change of about 104 BTUs per pound of refrigerant circulated; wherein the secondary stage sub-system has up to an enthalpy change of about 68 BTUs per pound of refrigerant circulated; and wherein the environmental test chamber further comprises a reheat exchange coil integral to the environmental test chamber.
According to yet another aspect of the invention, an environmental test chamber cooling system is disclosed. The environmental test chamber cooling system comprises: an environmental test chamber having a fast cool down evaporator and fast heat up condenser coil, wherein the heat exchanger coil is selectively coupled either to receive a hot refrigerant gas flow or to receive a sub-cooled refrigerant flow; a refrigeration sub-system coupled to the heat exchanger coil; a thermal storage unit coupled to the refrigeration sub-system; wherein the environmental test chamber has an operational temperature down to about xe2x88x92125xc2x0 F.; and wherein the sub-cooled refrigerant flow cools the environmental test chamber down to about xe2x88x92125xc2x0 F.; and wherein the refrigerant has an enthalpy change between about 68 to 104 BTUs per pound of refrigerant circulated.